eLFH - Heat and Temperature

Question 1

Temperature dependent enzymatic reactions mechanism

Answer 1

Increase in temperature leads to reacting molecules gaining kinetic energy

Increases likelihood of collision between enzyme and substrate

Thus increases rate of reaction

Question 2

Explanation for there being an optimal temperature for temperature dependent enzymatic reactions

Answer 2

There is a temperature at which an enzyme’s catalytic activity is greatest

Above that temperature, enzyme structure begins to denature

Question 3

Optimal temperature for temperature dependent enzymatic reactions

+ exception to this

Answer 3

37.0 degrees Celsius

Except enzymes in testes which function optimally at slightly lower temperature

Question 4

Energy definition

Answer 4

Ability to do work

Can be mechanical, chemical, electrical or thermal

Question 5

Heat (or heat energy) definition

Answer 5

Total energy of molecular motion in a substance

Cannot be directly measured

Question 6

Heat equation

Answer 6

Equation for Kinetic energy

Kinetic energy = 1/2 Mass x Velocity^2

Question 7

Factors which Heat / Heat energy depends on

Answer 7

Kinetic energy of molecules of a substance

Physical state of the substance

Number of molecules in the substance (i.e its mass)

Question 8

Temperature definition

Answer 8

Average kinetic energy of atoms which make up a substance

When temp is measured in Kelvin, it is directly proportional to average kinetic energy of molecules in the substance

Question 9

Relationship between heat energy and temperature

Answer 9

Temperature is measure of likelihood that one substance will transfer heat energy to another

Eg. Iceberg has higher amount of heat energy than pan of boiling water (due to its mass) but boiling water is higher temperature and would transfer heat energy to iceberg

Question 10

Specific heat capacity definition

Answer 10

Amount of heat energy required to raise temperature of 1 kg (a unit mass) of a substance by 1 Kelvin (a unit temperature rise)

Question 11

Specific heat capacity Equation

Answer 11

Question 12

Units of specific heat capacity

Answer 12

kJ / kg / K

can also be as kcal / kg / K

Question 13

Conversion of kJ to kcal

Answer 13

1 kcal = 4.18 kJ

Question 14

Heat capacity definition

Answer 14

Amount of heat energy required to raise the temperature of a given OBJECT by 1 Kelvin

I.e Heat capacity = Specific heat capacity x Mass of object

Question 15

Units of heat capacity

Answer 15

kJ / K

Question 16

Heat transfer from one object to another equation

Answer 16

Amount of heat transferred = Mass x Change in temperature x Specific heat capacity

Question 17

How to calculate temperature change when blood / fluid transfused

Answer 17

Amount of heat gained by infusion = amount of heat lost by body (amount of heat transferred)

Therefore can rearrange equation for new temperature (not change in temperature if temp for warmer object is Old temp - New temp, and for cooler object is New temp - Old temp)

Question 18

Heat transfer definition

Answer 18

Passage of energy from a warmer object to a cooler object

Question 19

Methods of heat transfer

Answer 19

Radiation 40%
Convection 30%
Evaporation 20%
Respiration 10%
(Conduction - minimal, 3-5%)

Royal College Exam Room Chat

Question 20

Reasons for conduction being a limited area of heat loss for patient in operating theatre

Answer 20

Air around patient is poor heat conductor

Table is well insulated

Contact area between patient and table relatively small

Question 21

Conduction mechanism

Answer 21

Heat transfer due to collision of molecules of two substances

Molecules’ kinetic energy transferred from higher temp substance to lower temp substance

Question 22

Convection definition

Answer 22

Transfer of heat by circulation through gas or liquid

Question 23

Convection mechanism with patient in operating room

Answer 23

Patient on table surrounded by air
Air warmed by conduction of heat from patient
As air increases in temp, becomes less dense and rises
Replaced by less dense cooler air
Cycle repeats creating convection current

Continues until equilibrium of temperature reached

Question 24

How radiation differs from convection and conduction

Answer 24

Does not require matter to transfer heat (eg method of sun heating the earth)

Question 25

Radiation mechanism

Answer 25

All objects above 0 Kelvin emit radiation as electromagnetic waves

Amount radiation emitted vs absorbed is a function of the object’s temperature

Waves falling within infrared spectrum are felt as heat

Question 26

Stefan-Boltzmann Law

Answer 26

Relates total amount of radiation emitted by an object to its temperature

Question 27

Evaporation mechanism of heat loss

Answer 27

Latent heat of vaporisation is taken from body to vaporise water / liquid

Can be described in terms of the other methods of heat loss
E.g Conduction from body to fluid causing evaporation. heat carried away by convection

Question 28

Evaporation heat loss from patient in theatre

Answer 28

Sweat or antiseptic solution evaporating from skin

Fluid evaporates from exposed moist internal body cavities

Question 29

Respiration heat loss

Answer 29

8% humidification
2% warming of inspired gases

Occurs via combination of other modes of heat transfer